The investigation whose preliminary results are reported herewith, was meant to ascertain the functional properties of S_II neurones receiving callosal projections. Electrophysiological experiments were performed in 9 chloralose-anaesthetized, curarized cats. By means of glass micropipettes the electrical activity from 71 S_II neurones was recorded. Each neurone has been tested with the stimulation of the peripheral receptive fields in order to classify the neuronal sample in lemniscal (Group I), extralemniscal (Group II) and unreactive (Group III) units. Sixty-seven units of the sample were further tested with electrical stimulation of contralateral S_I, S_II and ALA (anterior lateral associative) areas whereas the remaining 7 units were tested with the stimulation of the corpus callosum. From the data available it appears that, with the exception of one unit excited from contralateral ALA, only impulses set up in S_I and S_II were effective in eliciting excitation or inhibition of contralateral S_II neurones. It appears moreover that, on some occasions, impulses from both areas converge on the same unit. The sign of the commissural effect, i.e. excitatory or inhibitory, is in general related to the kind of peripheral reactivity of the unit on which the effect is exerted. In fact, out of 5 inhibited units, 4 belonged to Group I, whereas among the 24 excited units, 23 pertained to Group II. No unit of Group III reacted to commissural impulses. The latency of the discharges to cortical and callosal stimulation allows one to regard most of the described effects as mediated through the corpus callosum.